I want to say ESTj by association (shares a similar look with my mother), but her expressions seem introverted. SLI is a possibility.

God, I hope she isn't SLI (ISTp - right?)... That would be a disaster 'cause I am very close to eventually placing in ENFj... And we always had close to perfect understanding.

Yes, SLI is ISTp. But you look quite obviously introverted to me, and INFj does seem like the best option by far. ISTps and INFjs share a relation of Activity, which is probably the 2nd most compatible relationship in all of socionics (after duality).

But, for a certainty, back then,
We loved so many, yet hated so much,
We hurt others and were hurt ourselves...

Yet even then, we ran like the wind,
Whilst our laughter echoed,
Under cerulean skies...